Neuronal Communication 2

Question 1

What are the types of synapses, and how do they differ?

Answer 1

1. Axodendritic synapses: Target dendrites.
2. Axosomatic synapses: Target the cell body; have a larger effect than axodendritic.
3. Axoaxonic synapses: Target the axon; function as a gate to modify the nerve impulse.

Question 2

How do neurons communicate with each other across a synapse?

Answer 2

1. Neuronal communication: Signal travels from dendrites → cell body → axon.
2. Heart muscle cells: Connected by gap junctions for coordinated contraction.
3. Synaptic transmission: Ca²⁺ entry triggers exocytosis of neurotransmitters, which diffuse across the synaptic cleft to activate the postsynaptic cell.
4. Termination of signal: Glial cells have transporters to remove neurotransmitters, or acetylcholinesterase degrades acetylcholine. Passive diffusion or uptake by blood vessels may also occur.

Question 3

What is the role of graded potentials in synaptic communication?

Answer 3

Graded potentials: Local depolarization that diminishes with distance.

• Ripple effect: Like a ripple in water, the signal weakens as it travels along the membrane.

• Action potential: Triggered if depolarization reaches the axon hillock and hits the threshold.

Question 4

What is spatial summation and how does it contribute to action potential generation?

Answer 4

Spatial summation: Multiple synapses fire simultaneously, their signals combine to form a large enough depolarization to reach the threshold and trigger an action potential.

Question 5

What is temporal summation and how does it affect action potential firing?

Answer 5

Temporal summation: Synapses fire at different times but close enough for their signals to overlap, helping reach threshold and trigger an action potential.

Question 6

How do EPSP and IPSP influence action potential firing?

Answer 6

EPSP (Excitatory Postsynaptic Potential): Causes depolarization, making an action potential more likely.

• IPSP (Inhibitory Postsynaptic Potential): Causes hyperpolarization, making an action potential less likely.

• Balance: EPSP and IPSP can cancel each other out if they occur simultaneously.

Question 7

How do K⁺ ions contribute to hyperpolarization in neurons?

Answer 7

K⁺ ions: More concentrated inside the cell than outside. When K⁺ streams out, it causes hyperpolarization of the membrane, making it more negative.

Question 8

What are the different types of receptors at synapses?

Answer 8

Ionotropic receptors: Ligand-activated, fast-acting, open and close quickly to generate postsynaptic potentials.

• EPSP: Na⁺ (depolarization).

• IPSP: Cl⁻, K⁺ (hyperpolarization).

• Metabotropic receptors: Slow-acting, G-protein coupled, resulting in longer-lasting and varied responses.

Question 9

What is the function of inhibitory interneurons between sensory and motor neurons?

Answer 9

Inhibitory interneurons (glycinergic synapse): Prevent the effector from firing, ensuring proper regulation of reflexes and actions.

Question 10

Knee jerk reflex steps

Answer 10

Reflex hammer hits patellar tendon, stretch receptors in quadriceps femoris muscle are activated, action potential travels along afferent sensory axon that enters spinal cord through dorsal root, synapses onto a motor neuron on ventral horn on spinal cord, incoming signals result in firing at synapse and excitation of motor neuron, which projects an axon that exits spinal cord ventrally and terminates on homonymous quadriceps femrisj muscle, firing along efferent motor fibre results in excitation and contraction of it. Reflex kick

Question 11

What doesn’t terminate trans synaptic signalling

Answer 11

Neutralization of neurotransmitter by endogenous antibodies

Question 12

Cell bodies of what neurons lie outside cns

Answer 12

Sensory

Question 13

What do EPSP and IPSP do if they reach axon hillock at same time

Answer 13

Spatially summate